Reading module and image reading device and image forming apparatus therewith

ABSTRACT

A reading module has a light source, an optical system imaging, as image light, reflected light of light radiated from the light source to a document, a sensor where a plurality of imaging regions for converting the image light imaged by the optical system into an electrical signal are arranged next to each other in the main scanning direction, and a housing the light source, the optical system, and the sensor. The optical system has a mirror array where a plurality of reflection mirrors whose reflection surfaces are aspherical concave surfaces are coupled together in an array in the main scanning direction, and an aperture stop portion adjusting the amount of the image light reflected from the reflection mirror. The amount of the image light striking the reflection mirror is increasingly small from opposite end parts of the reflection mirror toward its central part in the main scanning direction.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromthe corresponding Japanese Patent Application No. 2016-232303 filed onNov. 30, 2016, the entire contents of which are incorporated herein byreference.

BACKGROUND

The present disclosure relates to a reading module that is incorporatedin digital copiers, image scanners, and the like and that readsreflected image light of the light radiated to a document, and to animage reading device and an image forming apparatus incorporating such areading module.

Conventional optical imaging systems for image reading devicesincorporated in multifunction peripherals and the like adopting anelectro-photographic process include a reduction optical system whereimages are formed on a reduced scale and a unity magnification opticalsystem where images are formed at unity magnification without beingreduced.

In the reduction optical system, a reduced image is formed on an imagesensor whose size is smaller than that of a document by use of aplurality of plane mirrors and an optical lens, and then the image isread. In the reduction optical system, as an image sensor, acharge-coupled device called a CCD sensor is used. The reduction opticalsystem advantageously has a deep depth of field. Here, the depth offield is the range in which, even when a subject (here a document) isdisplaced in the direction of the optical axis from the in-focusposition, the subject can be seen as if in focus. This means that, witha deep depth of field, even when the document is displaced from thepredetermined position, it is possible to obtain a satisfactory image.

On the other hand, the reduction optical system inconveniently has avery large optical path length (the distance light travels from asubject to the sensor) of 200 to 500 mm. In image reading devices, forthe purpose of securing the optical path length in a limited space in acarriage, the direction in which light travels is changed by use of aplurality of plane mirrors. This increases the number of componentsrequired, leading to an increased cost. When a lens is used in theoptical system, chromatic aberration occurs due to variation in therefractive index with wavelength. To correct the chromatic aberration, aplurality of lenses is required. As will be seen from the above, using aplurality of lenses becomes one of the factors that increase the cost.

In the unity magnification optical system, an image is read by beingimaged, with a plurality of erect-image rod-lenses with unitymagnification arranged in an array, on an image sensor whose size issimilar to that of a document. In the unity magnification opticalsystem, as an image sensor, a photoelectric conversion device calledCMOS (complementary MOS) sensor is used. The unity magnification opticalsystem advantageously has the following advantages. A smaller opticalpath length of 10 to 20 mm compared with the reduction optical systemhelps achieve compactness. Imaging by use of rod lenses alone eliminatesthe need for mirrors required in the reduction optical system. Thishelps make a scanner unit that incorporates a unity magnificationoptical system sensor slim. The simple construction helps achieve costreduction. On the other hand, the unity magnification optical system hasa very small depth of field, and thus when a document is displaced inthe direction of the optical axis from a predetermined position, asevere blur results from image bleeding due to different magnificationsof the individual lenses. As a result, it is inconveniently impossibleto uniformly read a book document or a document with an uneven surface.

In recent years, a method has been proposed in which, instead of thereduction optical system or the unity magnification optical systemdescribed above, an image is read by use of a reflection mirror array inthe imaging optical system. In this method, a plurality of reflectionmirrors is arranged in an array, and a document read in differentreading regions corresponding to the reflection mirrors on aregion-by-region basis is formed into an inverted image on a reducedscale on a sensor. Unlike in the unity magnification optical system thatuses a rod-lens array, one region is read and imaged with one opticalsystem. By adopting the telecentric optical system as the imagingsystem, when a document is read on a region-to region basis, no imagebleeding occurs as a result of images with different magnificationsoverlapping with each other; it is thus possible to suppress imageblurring and achieve a compound-eye reading method.

In this method, the optical system uses mirrors alone, and thus unlikein a case where the optical system uses a lens, no chromatic aberrationoccurs. This makes it unnecessary to correct chromatic aberration, andthus helps reduce the number of elements constituting the opticalsystem.

SUMMARY

According to one aspect of the present disclosure, a reading moduleincludes a light source, an optical system, a sensor, and a housing. Thelight source radiates light to a document. The optical system images, asimage light, reflected light of the light radiated from the light sourceto the document. In the sensor, a plurality of imaging regions forconverting the image light imaged by the optical system into anelectrical signal are arranged next to each other in the main scanningdirection. The housing houses the light source, the optical system, andthe sensor. The optical system includes a mirror array, a plurality ofaperture stop portions, and a plurality of light amount adjustingportions. In the mirror array, a plurality of reflection mirrors whosereflection surfaces are aspherical concave surfaces are coupled togetherin an array in the main scanning direction. The aperture stop portionsare each arranged in the optical path of image light between areflection mirror and an imaging region, and adjusts the amount of imagelight reflected from the reflection mirror. The amount of image lightthat strikes the reflection mirror is increasingly small from oppositeend parts of the reflection mirror toward its central part in the mainscanning direction.

Further features and advantages of the present disclosure will becomeapparent from the description of embodiments given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view showing the overall construction of animage forming apparatus incorporating an image reading portion that usesa reading module according to the present disclosure;

FIG. 2 is a side sectional view showing the internal structure of areading module according to one embodiment of the present disclosureincorporated in the image reading portion;

FIG. 3 is a partial perspective view showing the internal structure ofthe reading module according to the embodiment;

FIG. 4 is a sectional plan view showing, in a model where transmissionof rays of light is allowed, the configuration between an optical unitand a sensor in the reading module according to the embodiment;

FIG. 5 is a partly enlarged view showing the optical path between thereflection mirrors and the sensor in FIG. 4, showing how light travelingfrom outside reading regions is imaged on the sensor via the reflectionmirrors;

FIG. 6 is a partly enlarged view showing the optical path between thereflection mirrors and an imaging region on the sensor, showing aconfiguration where light shielding walls are provided at the boundariesof the imaging region;

FIG. 7 is a partly enlarged view showing the optical path between thereflection mirrors and the sensor in FIG. 4, showing the optical path oflight reflected from boundaries between the reflection mirrors;

FIG. 8 is a partial perspective view of an optical unit used in areading module according to a first embodiment of the presentdisclosure;

FIG. 9 is a perspective view of a light amount adjusting member providedin the optical unit;

FIG. 10 is a diagram, obtained by simulation, showing the difference inlight amount distribution among imaging regions on the sensor in themain scanning direction with and without the light amount adjustingmember;

FIG. 11 is a partial perspective view of an optical unit used in areading module according to a second embodiment of the presentdisclosure;

FIG. 12 is a partial perspective view of a light source and a mirrorarray used in a reading module according to a third embodiment of thepresent disclosure;

FIG. 13 is a diagram, obtained by simulation, showing the difference inlight amount distribution among imaging regions on the sensor in themain scanning direction with LEDs arranged on the substrate;

FIG. 14 is a partial perspective view of a light source and a mirrorarray used in a reading module according to a fourth embodiment of thepresent disclosure; and

FIG. 15 is a partial sectional view showing a modified example of thereading module according to the first embodiment, showing aconfiguration where image light is reflected three times on a turningmirror.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. FIG. 1 is a diagram showingan outline of the construction of an image forming apparatus 100incorporating an image reading portion 6 that uses a reading module 50according to the present disclosure. In the image forming apparatus 100shown in FIG. 1 (here a digital multifunction peripheral is taken as anexample), a copy operation proceeds as follows. In the image readingportion 6, which will be described later, document image data is readand is converted into an image signal. On the other hand, in an imageforming portion 3 in a multifunction peripheral main body 2, aphotosensitive drum 5 that rotates in the clockwise direction in FIG. 1is electrostatically charged uniformly by a charging unit 4. Then, by alaser beam from an exposure unit (such as a laser scanner unit) 7, anelectrostatic latent image is formed on the photosensitive drum 5 basedon the document image data read in the image reading portion 6. Then,developer (hereinafter, referred to as toner) is attached to the formedelectrostatic latent image by a developing unit 8, and thereby a tonerimage is formed. Toner is fed to the developing unit 8 from a tonercontainer 9.

Toward the photosensitive drum 5 having the toner image formed on it asdescribed above, a sheet is conveyed from a sheet feeding mechanism 10via a sheet conveyance passage 11 and a registration roller pair 12 tothe image forming portion 3. The sheet feeding mechanism 10 includessheet feed cassettes 10 a and 10 b and a stack bypass (manual feed tray)10 c arranged over the sheet feed cassettes 10 a and 10 b. When theconveyed sheet passes through a nip between the photosensitive drum 5and a transfer roller 13 (image transfer portion), the toner image onthe surface of the photosensitive drum 5 is transferred to the sheet.Then, the sheet having the toner image transferred to it is separatedfrom the photosensitive drum 5, and is conveyed to a fixing portion 14,which has a fixing roller pair 14 a, so that the toner image is fixedthere. The sheet having passed through the fixing portion 14 isdistributed among different conveyance directions by passage switchingmechanisms 21 and 22 arranged at branch points in a sheet conveyancepassage 15. The sheet is then, as it is (or after being conveyed to areverse conveyance passage 16 and being subjected to two-sided copying),discharged onto a sheet discharge portion composed of a first dischargetray 17 a and a second discharge tray 17 b.

After toner image transfer, toner left unused on the surface of thephotosensitive drum 5 is removed by a cleaning device 18. Electriccharge remaining on the surface of the photosensitive drum 5 is removedby a destaticizer (unillustrated) arranged on the downstream side of thecleaning device 18 in the rotation direction of the photosensitive drum5.

In an upper part of the multifunction peripheral main body 2, the imagereading portion 6 is arranged, and a platen (document presser) 24 isopenably/closably provided that presses and thereby holds a documentplaced on a contact glass 25 (see FIG. 2) of the image reading portion6. On the platen 24, a document conveyance device 27 is provided.

In the multifunction peripheral main body 2, a control portion (CPU) 90is arranged that controls the operation of the image forming portion 3,the image reading portion 6, the document conveyance device 27, and thelike.

FIG. 2 is a side sectional view showing the internal structure of areading module 50 according to one embodiment of the present disclosureincorporated in the image reading portion 6. FIG. 3 is a perspectiveview of the reading module 50 according to this embodiment, showing theoptical path from a document 60 to a sensor 41. FIG. 4 is a sectionalplan view showing the configuration between an optical unit 40 and thesensor 41 in the reading module 50 according to this embodiment.Although a mirror array 35 constituting the optical unit 40 shown inFIG. 4 reflects rays of light, for the sake of convenience ofdescription, FIG. 4 shows a model where the optical unit 40 transmitsrays of light.

The reading module 50 reads an image on the obverse side (lower side inFIG. 2) of the document 60 placed on the contact glass 25 while movingin the sub-scanning direction (the direction indicated by arrows A andA′). The reading module 50 also reads an image on the obverse side ofthe document 60 conveyed by the document conveyance device 27 (seeFIG. 1) while remaining at rest right under the automatic readingposition of the contact glass 25.

As shown in FIG. 2, the reading module 50 includes, in a housing 30thereof, a light source 31, a plane mirror 33 a, a turning mirror 34, amirror array 35 composed of a plurality of reflection mirrors whosereflection surfaces are aspherical surfaces, an aperture stop portion37, and a sensor 41 as a reading means. The sensor 41 is supported on asensor substrate 42 (see FIG. 4). As the sensor 41, a CCD or CMOS imagesensor is used according to the design. The reading module 50 has a homeposition right under a shading plate (unillustrated) for acquiring whitereference data.

With this configuration, to read a document image in a fixed-documentmanner, image reading proceeds as follows. First, a document 60 isplaced on the contact glass 25 with the image side down. Then, while theimage side of the document 60 is irradiated with light emitted from thelight source 31 and transmitted through an opening 30 a the readingmodule 50 is moved at a predetermined speed from the scanner home sideto the scanner return side. As a result, the light reflected from theimage side of the document 60, that is, the image light d (indicated bythe solid arrows in FIG. 2), has its optical path changed by the planemirror 33 a, and is then reflected on the turning mirror 34. Thereflected image light d is converged by the mirror array 35, isreflected again on the turning mirror 34, passes through the aperturestop portion 37, and is imaged on the sensor 41. The image light d ofthe formed image is, in the sensor 41, divided into pixels to beconverted into electrical signals commensurate with the densities ofindividual pixels.

On the other hand, to read a document image in a sheet-through manner,image reading proceeds as follows. The reading module 50 is moved toright under the image reading region (image reading position) of thecontact glass 25. Then, the image side of a document, which is conveyedone sheet after another while being lightly pressed against the imagereading region by the document conveyance device 27, is irradiated withlight from the light source 31. Then, the image light d reflected fromthe image side is imaged on the sensor 41 via the plane mirror 33 a, theturning mirror 34, the mirror array 35, the turning mirror 34, and theaperture stop portion 37.

As shown in FIG. 3, the mirror array 35 and the aperture stop portion 37are integrally formed of the same material and are integrated into aunit as the optical unit 40. By integrally forming the mirror array 35and the aperture stop portion 37, it is possible to hold the position ofthe mirror array 35 relative to the aperture stop portion 37 with highaccuracy. Thereby, it is possible to effectively prevent imagingperformance from degrading as a result of the relative position varyingwith expansion or contraction of the mirror array 35 and the aperturestop portion 37 due to change in temperature.

The turning mirror 34 is arranged at a position facing the mirror array35. The turning mirror 34 reflects both rays of light (the image lightd) which travel from the document 60 via the plane mirror 33 a to beincident on the mirror array 35 and rays of light (the image light d)which are reflected from the mirror array 35 to enter the aperture stopportion 37.

As shown in FIG. 4, the mirror array 35, which images the image light don the sensor 41, is composed of a plurality of reflection mirrors 35 a,35 b, 35 c . . . , which correspond to predetermined regions of thesensor 41, coupled together in an array in the main scanning direction(the direction indicated by arrows B and B′).

In the configuration according to this embodiment, the image light dreflected from reading regions Ra, Rb . . . (see FIG. 5) of the document60 separated in the main scanning direction has its optical path changedby the plane mirror 33 a and the turning mirror 34 (see FIG. 2), and isincident on the reflection mirrors 35 a, 35 b, 35 c . . . of the mirrorarray 35. The image light d is reduced at predetermined reductionmagnifications by the reflection mirrors 35 a, 35 b, 35 c . . . , isreflected again on the turning mirror 34, passes through the aperturestop portion 37, and is focused on corresponding imaging regions of thesensor 41 to form inverted images.

The inverted images formed on the imaging regions 41 a, 41 b . . . areconverted into digital signals, and thus magnification enlargementcorrection is performed through data interpolation according to thereduction magnifications for the respective imaging regions 41 a, 41 b .. . to reverse the data into erect images. Then, the images of theimaging regions 41 a, 41 b . . . are connected together to form anoutput image.

The aperture stop portion 37 is arranged at the focal points of thereflection mirrors 35 a, 35 b, and 35 c . . . constituting the mirrorarray 35. The physical separation distance (the distance in the up/downdirection in FIG. 2) between the aperture stop portion 37 and the mirrorarray 35 is determined according to the reduction magnification of themirror array 35. In the reading module 50 according to this embodiment,the turning mirror 34 reflects rays of light twice, and this makes itpossible to secure the optical path length from the mirror array 35 tothe aperture stop portion 37, and thus to minimize theincidence/reflection angle of the image light d with respect to themirror array 35. As a result, it is possible to suppress curvature ofimages formed in the imaging regions 41 a, 41 b . . . .

When the turning mirror 34 is divided into a plurality of mirrors, lightreflected by edge parts of the mirrors acts as stray light, and strikesthe mirror array 35 or enters the aperture stop portion 37. By using asingle plane mirror as the turning mirror 34 as in this embodiment, theeffect of stray light can be prevented even when both of the rays oflight overlap each other on the turning mirror 34. Although, in thisembodiment, the plane mirror 33 a is used to reduce the size of thereading module 50 in its height direction, it is also possible to adopta configuration where no plane mirror 33 a is used.

In a compound-eye reading method in which the mirror array 35 is used asin this embodiment, when the imaging magnification varies with theposition on a document (the optical path length between the reflectionmirrors and the document) within the region corresponding to thereflection mirrors 35 a, 34 b, 35 c . . . , when the document 60 floatsoff the contact glass 25, images overlap or separate from each other ata position next to border parts of the reflection mirrors 35 a, 35 b, 35c . . . , resulting in an abnormal image.

In this embodiment, a telecentric optical system is adopted between thedocument 60 and the mirror array 35. The telecentric optical system hasthe feature that the principal ray of the image light d that passesthrough the center of the aperture stop portion 37 is perpendicular tothe surface of the document. This prevents the imaging magnifications ofthe reflection mirrors 35 a, 35 b, 35 c . . . from varying even when thedocument position varies; it is thus possible to obtain a reading module50 having a deep depth of field that does not cause image bleeding evenwhen the document 60 is read in a form divided into fine regions. Toachieve that, the principal ray needs to remain perpendicular to thesurface of the document irrespective of the document position, and thisrequires a mirror array 35 whose size in the main scanning direction isequal to or larger than the size of the document.

In the compound-eye reading method in which the mirror array 35 is usedas described above, when the image light d reflected from the reflectionmirrors 35 a, 35 b, 35 c . . . and transmitted through the aperture stopportion 37 is imaged in a predetermined region on the sensor 41, theimage light d traveling from outside the reading region, may, as straylight, strike a region next to the predetermined region on the sensor41.

FIG. 5 is a partly enlarged view showing the optical path between thereflection mirrors 35 a and 35 b and the sensor 41 in FIG. 4. As shownin FIG. 5, the light from the reading regions Ra and Rb corresponding tothe reflection mirrors 35 a and 35 b is imaged in the correspondingimaging regions 41 a and 41 b on the sensor 41. Here, the rays of light(indicated by hatched regions in FIG. 5) inward of the principal ray,even though they belong to the light traveling from outside the readingregions Ra and Rb, are imaged on the sensor 41 by the reflection mirrors35 a and 35 b. Specifically, the light reflected from the reflectionmirror 35 a strikes the adjacent imaging region 41 b, and the lightreflected from the reflection mirror 35 b strikes the adjacent imagingregion 41 a. These parts of the image light, even though feeble, forminverted images corresponding to different reading regions, and thus, ifsuperimposed on proper images which are supposed to be formed in theimaging regions 41 a and 41 b, produce abnormal images.

Thus, in this embodiment, the imaging magnifications of the reflectionmirrors 35 a, 35 b, 35 c . . . of the mirror array 35 are set to bereduction magnifications, and as shown in FIG. 6, light shielding walls43 are formed to protrude from the boundaries between the imagingregions 41 a and 41 b of the sensor 41 in the direction of the aperturestop portion 37.

Here, as shown in FIG. 6, for example, of the image light d which is tobe imaged in the imaging region 41 a on the sensor 41, the lighttraveling from outside the reading region Ra is shielded by the lightshielding wall 43; it is thus possible to prevent the stray light fromstriking the imaging region 41 b arranged next to the imaging region 41a in the main scanning direction. Here, assuming that the reflectionmirrors 35 a, 35 b, 35 c . . . are set at a unity magnification, thereflection mirrors 35 a, 35 b, 35 c use the entire area over the imageforming regions 41 a, 41 b . . . up to their boundaries to form imagesof the image light d. As a result, no space can be secured for formingthe light shielding walls 43 at the boundaries of the imaging regions 41a, 41 b . . . . To secure the space for forming the light shieldingwalls 43, it is necessary to set the imaging magnifications of thereflection mirrors 35 a, 35 b, 35 c . . . to be reduction magnificationsas described above.

The optical unit 40 that includes the mirror array 35 and the aperturestop portion 37 preferably is, with consideration given to the cost,formed of resin by injection molding. Accordingly, it is necessary todetermine the reduction magnifications with a predetermined margin, withconsideration given to expansion or contraction due to change intemperature around the reading module 50 (hereinafter, referred to asenvironmental temperature). However, reducing the reductionmagnifications of the reflection mirrors 35 a, 35 b, 35 c . . .necessitates, when a sensor 41 with cell sizes (imaging regions)corresponding to the magnifications is used, a higher resolution on thesensor 41, and even when a sensor 41 with cell sizes for use in unitymagnification optical systems is used, a lower resolution results. Thus,it is preferable to maximize the reduction magnifications.

FIG. 7 is a partly enlarged view showing the optical path between thereflection mirrors 35 a and 35 b and the sensor 41 in FIG. 4. As shownin FIG. 7, the light reflected at the boundary between the reflectionmirrors 35 a and 35 b is distributed in opposite directions in the mainscanning direction, and passes respectively through aperture stopportions 37 to strike the imaging regions 41 a and 41 b on the sensor 41corresponding to the reflection mirrors 35 a and 35 b to be imaged.Here, comparing the amounts of light observed at a central part and atan end part of the imaging regions 41 a and 41 b reveals that the amountof light observed at the end part is a half (about 50%) of the amount oflight observed at the central part. Thus, in the reading module 50according to the present disclosure, there is provided a light amountadjusting member 70 which adjusts the amount of incident light whichstrikes the imaging regions 41 a, 41 b . . . on the sensor 41.

FIG. 8 is a partial perspective view of an optical unit 40 used in areading module 50 according to a first embodiment of the presentdisclosure. FIG. 9 is a perspective view of the light amount adjustingmember 70 provided in the optical unit 40. As shown in FIG. 8, in themain scanning direction in which the reflection mirrors 35 a, 35 b, 35 c. . . of the mirror array 35 are continuously arranged, as many lightamount adjusting members 70 as the number of the reflection mirrors 35a, 35 b, 35 c . . . are continuously formed. FIG. 9 shows only one unitof the light amount adjusting members 70 corresponding to one of thereflection mirrors 35 a, 35 b, 35 c . . . . FIG. 8 shows only fivereflection mirrors 35 a to 35 e of the mirror array 35.

As shown in FIGS. 8 and 9, the light amount adjusting member 70 iscomposed of a first light shielding portion 71 a arranged on the mirrorarray 35 side and a second light shielding portion 71 b arrangedopposite the first light shielding portion 71 a across a predeterminedinterval. The first light shielding portion 71 a and the second lightshielding portion 71 b are coupled together at opposite end parts of themirror array 35 in its longitudinal direction. A slit 72 formed betweenthe first light shielding portion 71 a and the second light shieldingportion 71 b has the largest width D at opposite end parts in the mainscanning direction (the direction indicated by arrows B and B′), thewidth D becoming increasingly small toward a central part. In thisembodiment, the slit 72 is given a width D of 2.7 mm at the opposite endparts in the main scanning direction and a width D of 1.0 mm at thecentral part in the main scanning direction.

The image light d reflected from the document 60 has its optical pathchanged by the plane mirror 33 a, and then passes through the slit 72 inthe light amount adjusting member 70. Here, the amount of light at thecentral part in the main scanning direction at which the width D of theslit 72 is small is restricted as compared with that at the opposite endparts. The image light d having passed through the slit 72 is reflectedon the turning mirror 34, and then strikes the reflection mirrors 35 a,35 b, 35 c . . . of the mirror array 35.

As described above, the light reflected from the boundaries between thereflection mirrors 35 a, 35 b, 35 c . . . is distributed among theimaging regions 41 a, 41 b . . . on the sensor 41 to be imaged; thus theamount of the image light d imaged on opposite end parts of the imagingregions 41 a, 41 b . . . in the main scanning direction is smaller thanthat on a central part thereof. However, the image light d haspreviously passed through the light amount adjusting member 70, and thusthe amount of light at the central part is smaller than that at theopposite end parts in advance.

FIG. 10 is a diagram, obtained by simulation, showing the difference inlight amount distribution among the imaging regions 41 a, 41 b . . . onthe sensor 41 in the main scanning direction with and without the lightamount adjusting member 70 shown in FIGS. 8 and 9. In FIG. 10, thehorizontal axis of the diagram represents the position of the imagingregions 41 a, 41 b . . . in the main scanning direction, with 0 mm atthe center of the imaging regions. The vertical axis represents theamount of light in the rays of light that strike the imaging regions 41a, 41 b . . . . Here, the result obtained when no light amount adjustingmember 70 is provided is represented by a broken line, and the resultobtained when the light amount adjusting member 70 is provided isrepresented by a solid line.

FIG. 10 reveals the following. When the light amount adjusting member 70is provided, the difference between the amounts of light at the centralpart and at the opposite end parts of the imaging regions 41 a, 41 b . .. is small; that is, the amounts of the image light d imaged on theimaging regions 41 a, 41 b . . . are equalized in the main scanningdirection. Thus, it is possible to effectively suppress imagedegradation resulting from the difference in noise between the centralpart and the end parts of images read in the imaging regions 41 a, 41 b. . . .

In this embodiment, the light amount adjusting member 70 is integrallyformed with the mirror array 35. Thus, the light amount adjusting member70 expands and contracts at the same rate as the mirror array 35 as itexpands and contracts due to change in temperature, and thus it ispossible to keep high positional accuracy between the reflection mirrors35 a, 35 b, 35 c . . . and the corresponding light amount adjustingmembers 70. Thus, it is possible to suppress vignetting of rays of lightresulting from variation in the positional accuracy of the light amountadjusting members 70, and also to effectively suppress variation in theamount of light at the central part and at the opposite end parts of theimaging regions 41 a, 41 b . . . in the main scanning direction.

FIG. 11 is a partial perspective view of an optical unit 40 used in areading module 50 according to a second embodiment of the presentdisclosure. In this embodiment, the light amount adjusting member 70 isformed integrally with a bottom surface 30 b of the housing 30.Otherwise, the structure of the reading module 50 is similar to that inthe first embodiment.

In this embodiment, the image light d having passed through the lightamount adjusting member 70 has a smaller amount of light at the centralpart in the main scanning direction than that at the opposite end partsin advance; thus, the amounts of the image light d imaged on the imagingregions 41 a, 41 b . . . are equalized in the main scanning direction.Thus, as in the first embodiment, it is possible to effectively suppressimage degradation resulting from the difference in noise between thecentral part and the opposite end parts, in the main scanning direction,of images read in the imaging regions 41 a and 41 b.

The light amount adjusting member 70 is formed integrally with thebottom surface 30 b of the housing 30, and this simplifies theconfiguration of the optical unit 40 as compared with the firstembodiment where the light amount adjusting member 70 is formedintegrally with the optical unit 40. This facilitates masking operationwhen the mirror array 35 is formed by vapor deposition. Also the surfaceaccuracy of the mirror array 35 is improved when the optical unit 40 isformed of a resin material.

FIG. 12 is a partial perspective view of a light source 31 and a mirrorarray 35 used in a reading module 50 according to a third embodiment ofthe present disclosure. The light source 31 is composed of LEDs(light-emitting diode) 31 a and a substrate 31 b on which the LEDs 31 aare mounted. In this embodiment, on the substrate 31 b, the LEDs 31 aare arranged only at positions corresponding to the boundaries betweenthe reflection mirrors 35 a, 35 b, 35 c of the mirror array 35.

The light emitted from the LEDs 31 a of the light source 31 is reflectedon the document 60 as image light d. The image light d has its opticalpath changed by the plane mirror 33 a to be reflected by the turningmirror 34, and then strikes the reflection mirrors 35 a, 35 b, 35 c . .. of the mirror array 35.

As described above, the light reflected from the boundaries between thereflection mirrors 35 a, 35 b, 35 c . . . is distributed among theimaging regions 41 a, 41 b . . . on the sensor 41 to be imaged, and thusthe amount of the image light d imaged on the opposite end parts of theimaging regions 41 a, 41 b . . . in the main scanning direction issmaller than that on the central part. However, the LEDs 31 a arearranged only at the positions corresponding to the boundaries betweenthe reflection mirrors 35 a, 35 b, 35 c . . . , and thus, from thebeginning, the amount of image light d at the central part in the mainscanning direction is smaller than that at the opposite end parts.

FIG. 13 is a diagram, obtained by simulation, showing the difference inlight amount distribution among the imaging regions 41 a, 41 b . . . onthe sensor 41 in the main scanning direction with the LEDs 31 a arrangedon the substrate 31 b. In FIG. 13, the horizontal axis of the diagramrepresents the position of the imaging regions 41 a, 41 b . . . in themain scanning direction, with 0 mm at the center of the imaging regions.The vertical axis represents the amount of light in the rays of lightthat strike the imaging regions 41 a, 41 b Here, the result obtainedwhen the LEDs 31 a are evenly arranged also at positions correspondingto the central part of the reflection mirrors 35 a, 35 b, 35 c . . . isrepresented by a broken line, and the result obtained when the LEDs 31 aare arranged only at positions corresponding to the boundaries betweenthe reflection mirrors 35 a, 35 b, 35 c is represented by a solid line.

FIG. 13 reveals the following. When the LEDs 31 a are arranged only atthe positions corresponding to the boundaries between the reflectionmirrors 35 a, 35 b, 35 c . . . , the difference between the amounts oflight at the central part and at the opposite end parts of the imagingregions 41 a, 41 b . . . is small; that is, the amounts of the imagelight d imaged on the imaging regions 41 a, 41 b . . . are equalized inthe main scanning direction. Thus, it is possible to effectivelysuppress image degradation resulting from the difference in noisebetween the central part and the end parts of images read in the imagingregions 41 a, 41 b . . . .

FIG. 14 is a partial perspective view of a light source 31 and a mirrorarray 35 used in a reading module 50 according to a fourth embodiment ofthe present disclosure. In this embodiment, on the substrate 31 b, theLEDs 31 a are arranged such that their arrangement intervals areincreasingly small from the position corresponding to the central part,in the main scanning direction, of the reflection mirrors 35 a, 35 b, 35c of the mirror array 35 toward the positions corresponding to theopposite end parts. Otherwise, the structure of the reading module 50 issimilar to that in the third embodiment.

In this embodiment, the arrangement intervals between the LEDs 31 a atthe positions corresponding to the opposite end parts of the reflectionmirrors 35 a, 35 b, 35 c in the main scanning direction are smaller thanthose at the positions corresponding to the central part of thereflection mirrors 35 a, 35 b, 35 c in the main scanning direction. As aresult, from the beginning, the amount of image light d is smaller atthe central part in the main scanning direction than that at theopposite end parts; this reduces the difference between the amounts ofthe image light d at the central part and at the opposite end parts ofthe imaging regions 41 a, 41 b . . . . Thus, as in the third embodiment,it is possible to effectively suppress image degradation resulting fromthe difference in noise between the central part and the opposite endparts, in the main scanning direction, of images read in the imagingregions 41 a, 41 b . . . .

The embodiments described above are in no way meant to limit the presentdisclosure, which thus allows for many modifications and variationswithin the spirit of the present disclosure. For example, although inthe above-described embodiments, image light d which travels from thedocument 60 via the plane mirror 33 a to strike the mirror array 35 andimage light d which is reflected from the mirror array 35 to enter theaperture stop portion 37 are each reflected on the turning mirror 34once, that is, reflection on it takes place twice in total, as shown inFIG. 15, with a plane mirror 33 b arranged between the mirror array 35and the aperture stop portion 37, image light d may be reflected on theturning mirror 34 three times or more.

Although, in the above-described first and second embodiments, thesurfaces, which face each other, of the first light shielding portion 71a and the second light shielding portion 71 b constituting the lightamount adjusting member 70 are in the shape of arcs (curved surfaces) asseen from the direction of incidence of light, as long as they are insuch a shape as to reduce the amount of light at the central part in themain scanning direction as compared with that at the opposite end parts,the surfaces of the first light shielding portion 71 a and the secondlight shielding portion 72 b facing each other do not necessarily haveto be in the shape of arcs; they may instead be, for example, in theshape of triangles or trapezoids.

In the above-described fourth embodiment, there is no particularrestriction on the arrangement intervals between, and the number of, theLEDs 31 a, and thus, these can be set as necessary according to thenumber of the reflection mirrors 35 a, 35 b, 35 c . . . or theirdimension in the main scanning direction. Instead of the above-describedthird and fourth embodiments, as the LEDs 31 a arranged at the positionscorresponding to the boundaries between the reflection mirrors 35 a, 35b, 35 c . . . , ones having higher light emission intensity than that ofthe LEDs 31 a arranged at the positions corresponding to the centralpart of the reflection mirrors 35 a, 35 b, 35 c in the main scanningdirection may be used. Or, the voltage applied to the LEDs 31 a arrangedat the positions corresponding to the boundaries between the reflectionmirrors 35 a, 35 b, 35 c . . . may be set higher than the voltageapplied to the LEDs 31 a arranged at the positions corresponding to thecentral part of the reflection mirrors 35 a, 35 b, 35 c in the mainscanning direction.

By combining the configuration of the third and fourth embodiments,where the arrangement of the LEDs 31 a is adjusted, with that of thefirst and second embodiments, where the light amount adjusting member 70is provided, it is possible to effectively reduce the difference betweenthe amounts of light at the central part and at the opposite end partsof the imaging regions 41 a, 41 b . . . .

Although the above-described embodiments deal with, as an example of animage reading device, the image reading portion 6 incorporated in theimage forming apparatus 100, the present disclosure is applicableequally to an image scanner used separately from the image formingapparatus 100.

The present disclosure is applicable to image reading devices providedwith a reading module adopting a reading configuration where reflectionmirrors are arranged in an array. Based on the present disclosure, it ispossible to provide a reading module that can reduce the variation inthe amount of incident light on the imaging regions, in the mainscanning direction, on the sensor corresponding to the reflectionmirrors and that can effectively suppress image degradation resultingfrom the difference in noise between the central part and the oppositeend parts in the main scanning direction, and to provide an imagereading device and an image forming apparatus provided with such areading module.

What is claimed is:
 1. A reading module comprising: a light source whichradiates light to a document; an optical system which images, as imagelight, reflected light of the light radiated from the light source tothe document; and a sensor in which a plurality of imaging regions forconverting the image light imaged by the optical system into anelectrical signal are arranged next to each other in a main scanningdirection, wherein the optical system comprises: a mirror array in whicha plurality of reflection mirrors whose reflection surfaces areaspherical concave surfaces are coupled together in an array in the mainscanning direction; a plurality of aperture stop portions each providedin an optical path of the image light between a reflection mirror and animaging region of the sensor, the plurality of aperture stop portionsadjusting an amount of the image light reflected from the reflectionmirror; and a light amount adjusting member having a slit through whichthe image light strikes the reflection mirror, the slit having a widthwhich is increasingly small from the opposite end parts of thereflection mirror toward the central part thereof in the main scanningdirection, and an amount of the image light that strikes the reflectionmirror is increasingly small from opposite end parts of the reflectionmirror toward a central part thereof in the main scanning direction. 2.The reading module of claim 1, wherein as many light amount adjustingmembers as the number of the reflection mirrors are continuouslyarranged in the main scanning direction.
 3. The reading module of claim1, wherein the light amount adjusting members are formed integrally withthe mirror array.
 4. The reading module of claim 1, wherein the lightamount adjusting members are formed integrally with a housing.
 5. Thereading module of claim 1, wherein the light source includes a substrateextending in the main scanning direction and a plurality oflight-emitting diodes mounted on the substrate, and an amount of light,in the main scanning direction, emitted from the light-emitting diodesis adjusted to be increasingly small from the opposite end parts of thereflection mirror toward the central part thereof in the main scanningdirection.
 6. The reading module of claim 5, wherein the light-emittingdiodes are arranged on the substrate only at positions corresponding toboundaries between the reflection mirrors.
 7. The reading module ofclaim 5, wherein the light-emitting diodes are arranged on the substratesuch that arrangement intervals thereof are increasingly small from aposition corresponding to the central part of the reflection mirror inthe main scanning direction toward positions corresponding to theopposite end parts.
 8. The reading module of claim 2, wherein an opticalpath of the image light traveling toward each reflection mirror and anoptical path of the image light traveling toward an aperture stopportion run in a same direction, and a turning mirror is arranged thatbends the image light reflected from the reflection mirror toward theaperture stop portion, and the turning mirror bends the image lighttwice or more times on a same reflection surface thereof, includingbending the image light traveling toward the reflection mirror andbending the image light reflected from the reflection mirror toward theaperture stop portion.
 9. The reading module of claim 1, wherein themirror array and the aperture stop portions are integrally formed. 10.The image reading device of claim 1, wherein the optical system is atelecentric optical system where the image light is parallel to anoptical axis on a document side of the mirror array, and forms aninverted image on the sensor.
 11. The image reading module of claim 10,wherein imaging magnifications of the reflection mirrors for therespective imaging regions are set at reduction magnifications, and alight shielding wall is provided which is formed to protrude from aboundary between adjacent imaging regions toward the aperture stopportions, the light shielding wall shielding stray light which is to beincident on the imaging regions.
 12. The image reading module of claim11, wherein image data read in the imaging regions of the sensorundergoes magnification enlargement correction through datainterpolation according to the reduction magnifications to reverse thedata into erect images, and then the images in the imaging regions areconnected together to form an output image.
 13. An image reading device,comprising: a contact glass fixed to a top surface of an image readingportion; a document conveyance device which is openable/closable upwardand downward with respect to the contact glass, the document conveyancedevice conveying a document to an image reading position of the contactglass; and the reading module of claim 1 arranged to be reciprocableunder the contact glass in a sub-scanning direction, wherein the readingmodule is capable of reading an image of a document placed on thecontact glass while moving in the sub-scanning direction, and thereading module is capable of reading an image of a document conveyed tothe image reading position while remaining at rest at the positionfacing the image reading position.
 14. An image forming apparatuscomprising the image reading device of claim 13.